FIGS. 19 and 20 show a conventional transmission guide 800 for use in the timing transmission of an automobile engine. The guide 800 comprises a shoe 810 on which a transmission chain C slides, and a base 820 separately molded and integrally assembled with the shoe 810 to support and maintain the configuration of the shoe. This transmission guide is disclosed in United States Patent Application publication No. 2005/0079938, published Apr. 14, 2005.
Another known chain guide, disclosed in Japanese laid-open Patent Application No. 2004-150615, dated May 27, 2004, comprises a base composed of primary synthetic resin and a shoe composed of secondary synthetic resin on which a transmission chain slides. The shoe has a back surface that is fused integrally with a supporting surface of the base after molding the base.
In the prior art transmission guide 800, vibration due to load variations causes the shoe 810 to move longitudinally through a distance corresponding to a margin allowed for assembly when the transmission chain slides on the surface 810a of the shoe. Therefore, each hook 814 of the shoe 810 locally abuts an end of a notch 824 in the base 820, causing an excessive concentration of stress in the hooks. The excessive stress can result in breakage of a hook, separation of the shoe from the base, and failure of the guide to maintain proper travel of the transmission chain.
In a chain guide in which the back of a synthetic resin shoe is fused to the base, it is difficult to maintain the bond between the shoe and the base over a long time because, when transmission chain is located eccentrically in the direction of the width of the guide, a widthwise shearing force can cause the shoe to separate for the base.
A chain guide is typically operated in a high temperature environment caused by circulation of hot engine oil as well as by sliding friction between the chain and the shoe. The base, which is composed of glass fiber-reinforced resin, and the shoe, which is composed of non-reinforced resin, expand and contract with changes in temperature, and, because the coefficient of thermal expansion of the non-reinforced resin of the shoe is larger than that of the glass fiber-reinforced resin of the base, the different rates of thermal expansion or contraction can also cause the shoe to separate from the base.
There is a need for a transmission guide that can be produced without an assembly step in which a synthetic resin shoe is attached to a synthetic resin base, and in which the strength of the bond between the shoe and the base is enhanced, and which accommodates the differences in the rates of thermal expansion and contraction of the shoe and the base.